Re: [PATCH v4 5/6] libxl: add options to enable/disable emulated devices

[Ian Campbell <ian.campbell@citrix.com>]

On Fri, 2016-01-22 at 18:04 +0100, Roger Pau Monné wrote:
> El 21/01/16 a les 17.51, Roger Pau Monne ha escrit:
> > Allow enabling or disabling emulated devices from the libxl domain
> > configuration file. For HVM guests with a device model all the emulated
> > devices are enabled. For HVM guests without a device model no devices
> > are
> > enabled by default, although they can be enabled using the options
> > provided.
> > The arbiter of whether a combination is posible or not is always Xen,
> > libxl
> > doesn't do any kind of check.
> > 
> > This set of options is also propagated inside of the libxl migration
> > record
> > as part of the contents of the libxl_domain_build_info struct, so that
> > when
> > the other end (restore) creates the domain the same set of devices are
> > enabled. This is important for future compatibility, in case we decide
> > to
> > enable some emulated devices by default for HVMlite guests, old HVMlite
> > guests migrated to newer versions should continue to see the same set
> > of
> > emulated devices.
> > 
> > It has been discussed that it would be better to avoid having this
> > information inside of the libxl stream, and to instead rely on which
> > devices
> > get their context loaded inside of Xen on resume. This of course
> > requires
> > more work and it also has certain issues, like the fact that some
> > devices
> > don't restore a context at all (like VGA). The consensus is that the
> > solution presented in this patch is not going to prevent further
> > developments in this direction, and can always be used as a check to
> > make
> > sure the Xen context and the libxl context are in sync.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > ---
> > Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> > Cc: Ian Campbell <ian.campbell@citrix.com>
> > Cc: Wei Liu <wei.liu2@citrix.com>
> 
> To tools committers:

Ack.

>  please refrain from pushing this until we have a
> clear view on which devices we might want to enable in the future.
> Adding a bunch of libxl options that are never going to be allowed
> doesn't make any sense.
> 
> Roger.
> 

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